Corrosion inhibiting system

ABSTRACT

AQUEOUS ACID SOLUTIONS ARE INHIBITED AGAINST CORROSION OF METALS, ESPECIALLY FERROUS METALS, BY INCORPORATION OF A CORROSION INHIBITING-SYSTEM COMPOSED OF A COMBINATION OF AN ACETYLENIC CARBINOL, AN ACETYLENIC GLYCOL, AND A SATURATED HETEROCYCLIC NITROGEN COMPOUND MIXTURE DERIVED FROM GILSONITE.

United States Patent Office 3,591,511 Patented July 6, 1971 3,591,511 CORROSION INHIBITING SYSTEM Morton W. Leeds, Murray Hill, N.J., assignor to Air Reduction Company, Incorporated, New York, NY. No Drawing. Filed Dec. 31, 1968, Ser. No. 788,999 Int. Cl. 023g 1/06 US. Cl. 152-148 3 Claims ABSTRACT OF THE DISCLOSURE This invention relates to the inhibition of metal corrosion in acidic solutions and is more particularly concerned with inhibited aqueous acid solutions suitable for the treatment of metals.

Metal cleaning baths and pickling baths generally comprise aqueous solutions of inorganic acids such as sulfuric acid, hydrochloric acid, and phosphoric acid, and are useful in the cleaning and treatment of iron, zinc, ferrous alloys, and the like.

In the use of aqueous acidic baths to treat metals, additives or inhibitors in the baths are desirable to prevent or inhibit corrosion or erosion of the metal surfaces. Similarly, in the field of oil-well acidizing, it is necessary to use inhibitors in order to prevent corrosion of the oilwell equipment by the aqueous acid solutions employed. Various other industrial operations also involve contact between an aqueous acidic solution and a metal, and an inhibitor must be used in order to minimize corrosion and/or consumption of the metal by such contact.

If no corrosion inhibitor is present when the aqueous acidic solution comes into contact with the metal, excessive metal loss, production of undesirable metal surface properties, excessive consumption or loss of acid, and like adverse results will be experienced. Many different types of inhibitors have been proposed, but there has been a continuing search for corrosion inhibitors which can be used effectively in small concentrations, and which are economical to produce, since the use of inhibitors is a necessary expense and it is economically prudent to keep this expense at a minimum while, at the same time, realizing the desired inhibition of metallic corrosion or consumption. The need is also for corrosion inhibitors which are effective at high temperatures, e.g. 200 F. and above, such as are encountered in various operations involving acidic solutions, particularly oil-well acidizing where higher and higher temperatures are encountered as the well extends further into the earth.

While various corrosion-inhibiting agents have been proposed, all of such agents are not of equal effectiveness and of the many hundreds of agents which have been contemplated, only a few are sufficiently active to be commercially attractive. This is particularly true in the case of high-temperature operations. Some inhibitors which have been proposed are reasonably effective at low and moderate temperatures, but fail completely when high temperatures are encountered.

There has, therefore, been a continuing search for more effective inhibitors, or for ways of making a given inhibitor more effective. This search has involved the discovery of combinations of inhibitors which act together to provide an inhibitor system. However, many of these systems involve relatively expensive components so that, while they may be relatively effective in their corrosioninhibiting activity, there are disadvantages from an economic standpoint, particularly if they have to be used in substantial quantities in order to bring about the desired corrosion-inhibiting activity. Similarly, many of these systems are ineffective at elevated temperatures. In particular, there is a need for a corrosion-inhibiting system comprising a plurality of components wherein relatively inexpensive compounds of poor corrosion-inhibiting action can be catalyzed or potentiated by the other component or components of the system so that the combination has a high corrosion-inhibiting activity even at elevated temperatures.

It is accordingly an object of this invention to provide a novel corrosion-inhibiting system involving a combination of agents which is highly effective from the standpoint of corrosion-inhibiting activity and which is, at the same time, commercially attractive.

It is a further object of this invention to provide a novel corrosion-inhibiting system comprising a combination of agents wherein one agent has a strong potentiating or catalyzing action upon the other agent so that the corrosion-inhibiting effectiveness of the combination is greater than the additive action of the components of the combination.

It is another object of the invention to provide a corrosion-inhibiting system of the character indicated which is effective at high temperatures.

In accordance with this invention, it has been discovered that the above and other objects can be achieved by the provision of a corrosion-inhibiting system comprising a combination of an acetylenic carbinol of the formula R-CHOHCECH, wherein R is a lower alkyl radical, i.e. containing up to 7 carbon atoms, which may form a straight chain or a branched chain, an acetylenic glycol of the formula RCHOHCEC-CHOHR, and a saturated heterocyclic nitrogen compound mixture derived from gilsonite. While any of the acetylenic carbinols and glycols falling within the above formulae are suitabe, 1- hexyn-3-ol, 4-ethyl-1-octyn-3-ol, 5-decyn-4,7-diol and 5,10- diethyl-7-tetradecyn-6,9-diol have been found to be particularly suitable. The saturated nitrogen compound mixture is obtained by the hydrogenation of the unsaturated heterocyclic nitrogen compound mixture directly derived from gilsonite which generally can have a distillation range of about 350 F. to about 700 F., but most suitably there are employed fractions cut from this overall range by fractional distillation and hydrogenated as will be described below. Hydrogenation does not appreciably change the distillation range of the mixtures. A hydrogenated mixture or fraction of gilsom'te-derived heterocyclic nitrogen compounds having a distillation range generally lying between about 350 F. and 600 F. is preferably used. All temperatures are at 760 mm. While the mixture is referred to as being composed of saturated heterocyclic nitrogen compounds, it will be understood that minor amounts of the corresponding unsaturated compounds may be present as a result of incomplete hydrogenation. The ratio between the two acetylenic alcohol components of the corrosion-inhibiting system may vary, but the best results are obtained with weight ratios ranging between 1:10 and 10:1, preferably 1:5 and 5:1, and most suitably between 1:2 and 2:1. The ratios between the carbinol and glycol in combination and the nitrogen compound mixture are similarly between 1:10 and 10:1, preferably 1:5 and 5 :1, and advantageously between 1:2 and 2: 1, by weight.

The acetylenic alcohol-heterocyclic nitrogen compound mixture inhibitor system of this invention is useful, in general, in the inhibition of corrosion of metal surfaces in contact with aqueous mineral acid solution, such as hydrochloric acid, sulfuric acid, and phosphoric acid, for example in the acidizing of oil wells, in electrolytic cleaning baths, and electrolytic refining of metals, as well as in metal cleaning and pickling baths. The use of the acetylenic alcohol-nitrogen compound mixture inhibitor system of this invention for corrosion inhibition of metals in aqueous mineral acid solutions in advantageous in that the acetylenic alcoholnitrogen compound mixture system can be employed as a corrosion inhibitor over a wide and useful concentration range. A further advantage of this inhibitor system is that it may be used at elevated temperatures to provide good corrosion inhibition, even when in relatively low concentration.

The most effective amount of the corrosion-inhibiting system to be used in accordance with this invention can vary, depending upon local operation conditions. Thus, the temperature and other characteristics of the acid corrosive system may have a bearing upon the amount of inhibitor to be used. The higher the temperature and/or the higher the acid concentration, the greater is the amount of corrosion inhibitor required to give optimum results. In general, however, it has been found that a concentration of the corrosion-inhibiting system of the invention between 0.01 and 2%, preferably between 0.01% to 1.2%, by weight of the aqueous acidic solution is an effective corrosion-inhibiting concentration, although higher concentrations can be used when conditions make them desirable, with a concentration between 0.05% to 0.75% by weight being of most general use, at elevated temperatures, e.g. in the neighborhood of 200 F. The acidic solution can be dilute or concentrated and can be of any of the concentrations used in treating metals, e.g. ferrous metals, or for operations involving contact of acidic solutions with such metals, e.g. oil-well acidizing, and the like, for example 5 to 80%. In most operations of the character indicated, acid concentrations of -l5% by weight are employed, and non-oxidizing inorganic acids are used. However, it is not intended to limit the invention to any specific use of acidic solutions or with respect to any specific metal or acid.

Gilsonite is a natural asphalt-like substance found in the Uinta Basin in Utah and, when coked by application of heat, which results in the distillation of volatile materials, produces an oily distillate as the temperature isincreased. This distillate has an overall boiling range of about 350 up to about 900, although most of it boils below 700, and when it is refined by treatment with sulfuric acid produces mixtures of heterocyclic nitrogen compounds. These mixtures are generally fractionally distilled to provide a series of fractions. Such fractions derived from the gilsonite distillate are sold by the American Gilsonite Company of Salt Lake City, Utah. One of these fractions, sold commercially under the trade designation GN-O is catalytically hydrogenated, and this hydrogenated fraction, which is sold under the trade designation GN-300, is suitable employed as one of the components of the system of this invention to provide the hydrogenated heterocyclic nitrogen compound content. The following are typical distillation ranges in F. (ASTM D-158):

G N-200 G N-300 Volume,

Volume, percent F.

percent F.

amines such as methyl-substituted pyrrole, indole, pyridine, and quinoline.

The method use to determine the inhibiting properties of the system of the invention employs test specimens or coupons. To prepare the coupons, they are wiped with acetone to remove any residual oils or grease, and pickled for one minute in 10% hydrochloric acid to eliminate any scale and surface film. After pickling, the coupons are dipped, in sodium bicarbonate solution, rinsed well in tape water, rinsed in distilled water, and finally dried with acetone. The clean and dry specimens are then weighed to the nearest 0.1 mg. In carrying out the evaluation, hydrochloric acid of 15% by weight concentration is used in order to duplicate oil-well acidizing conditions. The inhibitor system is added to 4 oz. test bottles, ml. of the acid then added to each bottle; and the mixture shaken vigorously. The bottles are suspended in a constant-temperature bath consisting of a bell jar filled with ethylene glycol and equipped with a stirrer. The temperature is regulated to maintain the samples at 200:2" F. The bottles are placed in the bath /2 hour before the test coupons are added to insure temperature equilibrium. The weighed coupons, in duplicate, are then supported on glass hooks in the test bottles and the bottles are covered with watch glasses during the testing period of 16 hours. At the end of the testing period, the bottles are removed from the bath, the coupons withdrawn, rinsed 'with water, sodium bicarbonate solution, distilled water, and dried in acetone, then weighed to measure weight loss. Corrosion-inhibiting properties are conveniently expressed as percent inhibition, using the following formula:

Percent inhibition wt. loss of blankwt. loss of test coupon wt. loss of blank Percent inhibition Original wt. test, coupon-wt. loss of test coupon original wt. test coupon The following experiments will serve to illustrate the effectiveness of the corrosion-inhibiting system of this in vention under severe corrosion conditions encountered in practical application:

EXAMPLE Using the testing procedure described above, and employing test coupons of mild steel 1 in. x 2 in. x in. in size, samples comprising 1-hexyn-3-ol and 5-decyn-4,7- diol in a 2:1 weight ratio and comprising 4-ethyl-l-octyn- 3-01 and 5,10-diethyl-7-tetradecyn-6,9-diol in a 3 :1 weight ratio were each admixed with a mixture of saturated heterocyclic nitrogen compounds as represented by a commercial fraction of the character described above, the acetylenic alcohol mixture and the nitrogen compound mixture in each sample being in 1:1 weight ratio with respect to each other and the combined mixtures were added to 15% hydrochloric acid, each sample being added in the amount of 0.5% by weight of the acid, and the inhibitor combinations evaluated for corrosion-inhibiting activity. At the same time a blank test, using the same acid but without any inhibitor, was made. The following results were obtained.

Inhibitor: Percent inhibition 16 hrs. 1-hexyn-3-ol+5-decyn-4,7-diol+GN-300 99 4 ethyl 1-octyn-3-ol+5,10-diethyl-7-tetradecyn-6,9-diol+GN-300 99 None The mixed inhibitor comprising the combination of 1- hexyn-3-ol and 5-decyn-4,7-diol with the saturated heterocyclic nitrogen compound mixture was again tested using only 0.25% based on the weight of the acid. Again a percent inhibition of 99+, after 16 hours of exposure was recorded. In a further test, using the inhibitor mixture containing 1-hexyn-3-ol, this mixture was tested at 200 F. in 10% HCl for 4 hours in the concentration of only 0.1% based on the weight of the acid. Again a percent inhibition of 99+ was realized.

While the inhibitor system of this invention can be prepared from individual quantities of acetylenic carbinols and acetylenic glycols, such as 1 hexyn-3-ol, 4-ethyl-loctyn-3-ol, 5-decyn-4,7-diol, and 1,10-diethyl-7-tetradecyn- 6,9-diol a particularly advantageous source of these carbinol-glycol combinations is the reaction mixture obtained by the ethynylation of the corresponding aldehyde, e.g. butyraldehyde or 2-ethylhexaldehyde with acetylene, using the Well-known reaction wherein an aldehyde and acetylene are reacted in the presence of a catalyst in an inert solvent medium, most commonly an ether, the reaction being carried out at various temperatures but which generally lie in the range of to 50 C. This reaction, which was originally proposed by Favorskii, and has been improved upon by several other workers, is well-described in the literature, and reference is made, for example, to the book Acetylenic Compounds by Thomas F. Rutledge (Reinhold Book Corp, 1968), especially pages 146 to 149, and to the footnotes referred to therein. In a typical operation the aldehyde and the acetylene are reacted in an acetal or an ether as the reaction medium at substantially atmospheric pressure at a temperature of 20 to 30 C., using solid KOH as catalyst in amounts which are substantially stoichiometric (usually slightly in excess) with respect to the aldehyde, the acetylene being in excess of the stoichiometric quantity. The thus-produced mixture, e.g. of 1 hexyn-3-ol and -decyn-4,7-diol or of 4-ethyl-1- 0ctyn-3-ol and 1,10-diethyl-7-tetradecyn-6,9-diol, will vary in composition somewhat, depending upon the specific reaction conditions, but the ratio of the carbinol to the glycol usually lies within the range of 5:1 to 1:4, and most commonly is about 1:1 to 2:1. The inert reaction medium is readily separated by distillation, but minor amounts of the solvent, e.g. up to 10% by weight or more, may be present and such presence does not interfere with the activity of the acetylenic hydroxy compounds. The mixture may also contain minor amounts of by-products produced by condensation, aldolization, or other reactions and are also unobjectionable. Such by-products may range up to 10% by weight but are usually less than about 5% by weight.

It will be understood that a reaction mixture of the character indicated is particularly attractive from a commercial standpoint since purification of the product of the ethynylation reaction is not required, yet the important benefits of the combination of an acetylenic carbinol with an acetylenic glycol in the system of this invention are realized in the critical area of corrosion inhibition, i.e. high acid concentrations and high temperatures. The results shown in the foregoing test data are obtained when such a reaction mixture is employed in providing the corrosioninhibiting system of this invention.

The above-described tests show the positive action of the combination of an acetylenic carbinol, and acetylenic glycol, and a mixture of saturated heterocyclic nitrogen compounds in accordance with this invention in inhibiting metal corrosion in an acid solution of high concentration at an elevated temperature only slightly below the boiling point of water, over a prolonged period of time, the components of the system being relatively inexpensive chemicals in the corrosion-inhibiting field. Corresponding results are obtained when other acetylenic carbinols and other saturated nitrogen compound mixtures within the definitions set forth above are employed in forming the inhibiting system of this invention.

The coupons used in the foregoing experiments were cut from a in. sheet of a mild steel having the following typical analysis: 0.15% max. carbon, 0.30-0.60% manganese, 0.04% phosphorus, 0.05% sulfur, the balance lI'OIl.

It will be apparent that various changes and modifications may be made in the operations described in the foregoing without departing from the scope of the invention as defined in the appended claims. It is intended, therefore, that all matter contained in the above description of the invention shall be interpreted as illustrative only and not as lirnitative.

I claim:

1. A metal corrosion-inhibitor system for use with aqueous mineral acids which consists of essentially of an acetylenic carbinol of the formula R-CHOHCECH, wherein R is a lower alkyl group, an acetylenic glycol of the formula RCHOHCECCHOHR, and a saturated heterocyclic nitrogen compound mixture derived from gilsonite and distilling within the range of about 350 F. and about 700 F. at 760 mm. Hg, said acetylenic carbinol and said mixture being in the relative Weight ratios of 1:10 and 10:1.

2. A corrosion-inhibited mineral acid consisting essentially of an aqueous solution of the mineral acid and a small but effective amount of a corrosion-inhibiting system consisting essentially of an acetylenic carbinol of the formula RCHOHC CH, wherein R is a lower alkyl group, an acetylenic glycol of the formula RCHOHCE CCHOHR and a saturated heterocyclic nitrogen compound mixture derived from gilsonite and distilling within the range of about 350 F. and about 700 F. at 760 mm. Hg, said acetylenic carbinol and said mixture being in the relative weight ratios of 1: 10 and 10:1.

3. A corrosion-inhibited acid as defined in claim 2, wherein said corrosion-inhibiting system is present in the amount of 0.01% to 2% by weight.

References Cited UNITED STATES PATENTS 3,107,221 10/1963 Harrison et al. 252-448 3,249,548 5/1966 Herman et al 252-148X 3,404,094 10/1968 Keeney 252148 3,432,527 3/1969 Malec et a1 252-392 MAYER WEINBLATI, Primary Examiner US. Cl. X.R. 

